This application claims the benefit of Japanese Applications 2001-306874, 2002-022440, and 2002-207367, filed Oct. 2, 2001, Jan. 30, 2002, and Jul. 16, 2002, respectively, the entireties of which are incorporated herein by reference.
The present invention relates to a contact sheet. More specifically, the invention relates to a contact sheet which provides an electrical connection between electronic devices (such as integrated circuits, cables, and printed circuit boards) with a low spring load while accommodating variations in the size of the electronic devices. The contact sheet is suitably used for various tests or for mounting electronic devices, has excellent durability and reliability over repeated or long-term use, and also facilitates a ZIF (zero insertion force) structure for electronic devices having spherical terminals.
In recent years, because of the demands for reduced sizes and higher speeds in the field of information processing equipment, the lead pitch in electronic devices, such as integrated circuits, is increasingly becoming finer. From this viewpoint, the mounting method is shifting from through-hole mounting to surface mounting, and the arrangement of terminals is shifting from a peripheral arrangement to grid arrays. As a result, ball grid array (BGA) devices and land grid array (LGA) devices are becoming the mainstream mounting features since they permit surface mounting, even for grid arrays.
Sockets or connectors are more often employed to provide an electrical connection between electronic devices in place of soldering because of the demand for a lead-free connection. Such a socket or a connector is used, for example, not only to test an integrated circuit, but also for replaceably mounting electronic devices to printed circuit boards.
In recent years, the increasing operating speed of electronic devices, such as MPUs or memories, requires such devices to have lower inductance and less self-heating at higher-speed clock operation. To meet these requirements, the contact structure of the connector placed between terminals of electronic devices, integrated circuits or boards, must reduce the distance over which currents pass and reduce the electrical resistance as much as possible. Furthermore, since the spread of mobile electronic equipment calls for electronic devices having a thinner shape, the connectors which are mounted in the above devices also are required to have a thinner shape. Therefore, a contact sheet which meets the demands for minimizing current pass and which has a thin shape, as mentioned above, is promising as a thin connector with a fine pitch.
Meanwhile, as a thin connector with a fine pitch, as well as the contact sheet above, a component called xe2x80x9can anisotropic conductive sheetxe2x80x9d has conventionally been used. For example, conductive sheets having conductive elastomers or metal wires arranged in an insulative elastomer are known (U.S. Pat. Nos. 3,862,790 and 4,295,700) as well as ones in which conductive particles are added (Japanese Unexamined Patent Publication No. 6-82521).
Furthermore, contacts with a structure for avoiding contact with ball tips while tearing oxide films on solder surfaces are known, such as one having Y-shaped contacts (Japanese Unexamined Patent Publication No. 9-21847), and one which is inserted in finger springs (U.S. Pat. Nos. 5,702,255 and 5,730,606).
Additionally, the more terminals an integrated circuit has, the more insertion force that is required. A contact sheet having a structure in which the foregoing force is reduced to zero, and where spherical terminals are pushed laterally later by using a lever or the like is also known (U.S. Pat. Nos. 5,578,870 and 5,637,008).
However, problems with anisotropic conductive sheets exist. If the mounted electronic device is warped, the displacement length of the spring portion in the conductive sheet is too short to compensate for the warp. In addition, if the mounted electronic device has many terminals, the excessive contact load required to obtain an electrical connection causes the electronic device to deform. Also, when the electronic device adopts a BGA, there are problems in that the oxide film on the solder surface is not torn, and the peak of the solder ball is easily crushed while connecting.
On the other hand, even though an electrical connection can be ensured with Y-shaped contacts, since a long cantilever is employed, the distance over which currents must pass is relatively long. When Y-shaped contacts are used as contacts for testing or mounting at high frequency, the inductance against high-speed clock operation or resistance increases and heat is generated. It is difficult, however, to reduce the length of such Y-shaped contacts.
The present invention has been made with a view toward solving the above problems, and an object thereof is to provide a contact sheet that enables reliable electrical contact between electronic devices under low spring load while accommodating variations in the size of the electronic devices, such as an integrated circuit, a cable, and a printed circuit board. The contact sheet is suitably used for various tests or for mounting an electronic device, has excellent durability and reliability over repeated and long-term use, and also facilitates a ZIF (zero insertion force) structure for an electronic device with spherical terminals.
In order to attain the above-mentioned purpose, as a result of extensive research, applicants discovered that changing the width of a cantilever contact according to the distribution of stress in the contact provides a sufficient contact load, sufficient displacement, superior durability, and reliability. That is, the contact sheet has good characteristics including a high resistance to permanent plastic deformation and provides a high quality connection without variation because plastic deformation does not occur in a contacting part of the contact after plating.
That is, the present invention provides a contact sheet for providing an electrical connection between two or more electronic devices having spherical terminals or planar terminals, comprising two insulative elastic substrate sheets having a plurality of through holes and a plurality of plate-shaped or wire-shaped conductive elastic contacts. One end of one side of each contact is inserted and fixed between two of the substrate sheets at one edge (fixed point) of a through hole, while the other end of the contact is a moveable, non-fixed end arranged to bend as a cantilever extending from the fixed point, such that it departs only a predetermined distance from a first surface of the contact sheet with respect to the fixed point when a load is added to the non-fixed end. The contact has a bending portion in roughly a central part of the length (long direction) of the contact, where the contact is bent to extend in an angular direction such that the non-fixed end is positioned at a predetermined distance from the surface of the contact sheet, and the width of the contact, which is substantially perpendicular to the length, is continuously varied to be wider at areas of the contact which are subjected to larger stress and narrower at areas of the contact which are subjected to smaller stress, according to the quantity of stress applied to each part of the contact when a load is applied to the non-fixed end.
When an electronic device is mounted on an outer (first) side of the contact sheet, a spherical terminal or a planar terminal of the electronic device applies a load to the non-fixed end of the contact, and the non-fixed end of the contact is pressed and wipes the surface of the spherical terminal or the planar terminal of the electronic device. Consequently, an electrical connection can be ensured between the contact and the electronic device. At the same time, the bending portion of the contact is warped by the stress applied thereto, and the bending portion is pressed against another electronic device mounted on a second side of the contact sheet, to ensure an electrical connection between the bending portion of the contact and the other electronic device. In that manner, two or more electronic devices are electrically connected to each other via the contact sheet of the present invention.
According to the present invention, the contact sheet includes a second surface, and the bending portion of the contact protrudes from the second surface of the contact sheet. The electronic devices connected to each other via the contact sheet of the present invention include one or more devices selected from the group consisting of integrated circuits, electronic parts, cables, printed circuit boards, connectors, microphones, motors, antennas, and speakers.
The contact sheet according to the present invention can be used when the spherical terminals or the planar terminals of the electronic devices are arranged in a grid pattern, by providing the contacts arranged in the same grid pattern.
According to the present invention, the width of the contact is preferably widest at the bending portion, and decreases gradually to be continuously narrower toward the non-fixed end from the bending portion, and is narrowest at the non-fixed end. Furthermore, the width decreases gradually to be continuously narrower from the bending portion to an intermediate portion of the contact between the bending portion and the fixed end, and the width then increases gradually to be continuously wider from the intermediate portion to the fixed end.
The contact of the present invention can have a V-shaped or U-shaped notch opening toward the non-fixed end which is positioned between the non-fixed end and a predetermined portion of the contact between the non-fixed end and the bending portion. The contact can also include a slit in the shape of a convex lens positioned at a predetermined portion of the contact between the fixed end and the bending portion.
The contact can also be formed to have a peripheral outline in the shape of a concave lens over a portion of the length of the contact between the fixed end and a predetermined portion of the contact between the fixed end and the bending portion.
The fixed end of the contact is preferably wider than the bending portion, and a portion of the fixed end can extend back toward the non-fixed end. The portion of the fixed end that extends back toward the non-fixed end can extend to a position near the center point of the overall length of the contact.
The non-fixed end of the contact can be separated into two cantilevers, each of which has a protrusion which is bent at an angle in a range of 20 to 90 degrees toward the planar terminal of an electronic device that the cantilever faces. The outer edge of the protrusion wipes the surface of the planar terminal of the electronic device, such that the contact and the electronic device can be securely electrically connected at the point where the contact resistance between the contact and the electronic device is reduced.
The bending portion of the contact can include one or more bumps facing the electronic device at a part of the bending portion where the electronic device is pressed, such that an outer edge of a bump presses on the electronic device, and the contact and the electronic device can be securely electrically connected at the point where the contact resistance between the contact and the electronic device is reduced.
Preferably, the contact has an effective length which can increase the amount of bending (displacement length) of the non-fixed end when a load is added to the non-fixed end of the contact, which acts as a cantilever extending from a fixed point (the fixed end of the contact).
The contact is preferably shaped to increase the amount of bending from the fixed end to the bending portion and reduce the amount of bending from the bending portion to the non-fixed end when a load is added to the non-fixed end of the contact.
According to one embodiment of the present invention, a complex of contact sheets is provided, wherein a plurality of contact sheets are bonded together via an adhesive sheet having through holes formed therethrough in the same pattern as that of the contact sheets. The contact sheets can be bonded directly via the adhesive sheet, and one of the substrate sheets of each of the contact sheets which would otherwise face the adhesive sheet can be removed or omitted such that the adhesive sheet directly adheres to each of the contacts. The adhesive sheet can be an anisotropic conductive film. A complex of contact sheets can also be provided, wherein a plurality of contact sheets are bonded via glue or soldering. One of the substrate sheets of each contact sheet can be removed or omitted such that the glue or soldering directly adheres to each of the contacts.